Interleukin-7 and -15 Maintain Memory T Helper 17 Cells in Dry Eye Disease

Abstract

Purpose : Memory T helper 17 (mTh17) cells have been found crucial in mediating the chronicity of various refractory autoimmune disorders, including dry eye disease (DED); however, the underlying mechanisms maintaining mTh17 cells have remained elusive. This study was designed to investigate whether interleukin (IL)-7 and IL-15 maintain mTh17 cells in chronic DED.

Methods : Chronic DED was induced by exposing C57BL/6 mice to desiccating stress using a controlled environment chamber for 14 days and then housing mice in a standard environment for additional 14 days. Expression of IL-7 receptor (IL-7R) and IL-15 receptor (IL-15R) by mTh17 cells (CD4⁺CD44^hiIL-17A⁺) derived from chronic DED mice was analyzed using flow cytometry. IL-7 and IL-15 mRNA and protein expressions in DED mice were quantified by real-time PCR and ELISA. In addition, draining lymph nodes isolated from chronic DED mice were cultured in the presence of IL-7, IL-15, IL-7 and IL-15, anti-IL-7 antibody (Ab), anti-IL-15 Ab, anti-IL-7 and anti-IL-15 Abs, or control IgG for 72 hours, and then examined for the frequencies of mTh17 cells using flow cytometry. Finally, therapeutic effects of topical neutralization of either IL-7, IL-15 or IL-17 were evaluated in chronic DED.

Results : mTh17 cells from chronic DED mice expressed IL-7R and IL-15R. IL-7 and IL-15 expression was significantly higher in chronic DED mice compared to normal mice at both mRNA (2-fold increase, p < 0.05) and protein (37.3±6.2 and 99.2±14.3, vs. 2.0±0.3 and 43.1±4.8, p < 0.05) levels in the conjunctiva. They were constitutively expressed at comparable levels in the DLNs of normal and DED mice. Furthermore, DLNs from chronic DED mice cultured in the presence of IL-7, IL-15, or IL-7 and IL-15 together, displayed higher frequencies of mTh17 cells (0.20±0.03%, 0.18±0.02%, 0.16±0.02%, respectively) compared with those cultured with anti-IL-7 Ab (0.057±0.002%), anti-IL-15 Ab (0.055±0.017%), anti-IL-7 and anti-IL-15 Abs together (0.081±0.006%), or control IgG (0.087±0.006%). Topical neutralization of ocular IL-7 or IL-15 effectively reduced DED severity and significantly suppressed frequencies of mTh17 cells in both conjunctiva and DLN, while topical neutralization of IL-17 did not affect mTh17 frequencies in the DLN.

Conclusions : These findings demonstrate that both IL-7 and IL-15 maintain mTh17 cells and could serve as novel therapeutic targets for chronic DED.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.